I’ve just been looking into an ancestor who lived here and I think I’ve worked out the answer.
Old Town which is the north of Kilsyth (or the top end as some call it today) is the original part of Kilsyth. Pretty self explanatory.
New town (known as the bottom end) was built to house “navvies” building the Glasgow - Edinburgh railway line in the 1840’s.
My ancestor John Bamford came over from Ireland to Kilsyth and lived here. His occupation was a general labourer. In that census he lived in the same house as his wife, Helen Currie and his 3 sons, John, David and Thomas and there were also another 6 young men who were also labourers from Ireland living in there and another young woman. I found this strange so looked it up. “Navvies” as they were known, would often live in hut-like accommodation which were over crowded a lot of the time.
Hopefully you found this helpful